Technical Abstract:
Commercial sugarbeet hybrids were evaluated for disease resistance to <i>Beet curly top virus</i> (BCTV) to examine if disease ratings taken in an artificially inoculated nursery correlate with improved disease resistance and yield in commercial fields exposed to natural disease incidence. For this study, 29 hybrids were planted in a nursery in Kimberly, ID, and in a commercial, sprinkler-irrigated field in Nampa, ID in 2004. Plants were evaluated for BCTV using a Disease Index (DI) scale of 0 (no symptoms) to 9 (dead). The moderately severe and uniform disease in the Nampa field resulted in significant differences among hybrids for DI, root yield, sugar content, and estimated recoverable sugar. The disease ratings were positively correlated (r = 0.91, <i>P</i> < 0.0001) with ratings from the Kimberly nursery. In the commercial field, the regression line for estimated recoverable sugar versus DI indicated that yield was related to disease severity (r<sup>2</sup> = 0.54, <i>P</i> < 0.0001). For each unit increase in DI (increasing susceptibility), there was a decrease of 957.53 lb of estimated recoverable sugar/A. These data confirm results obtained in 1992 from a commercial variety trial in Ontario, OR, and a curly top disease nursery. Thus, curly top nurseries can be used to select BCTV-resistant hybrids for commercial cultivation.